This invention relates to a data linking system for a plurality of programmable controllers.
Recently, a programmable controller, or sequence controller, has been widely utilized for working, assembling, deliverying and the like operations of a machine control with the development of computer utilizing techniques. With these operative controls, only one programmable controller controls the whole system in a conventional system of this field of art, but it has become impossible to control the whole system with one programmable controller because of the requirements of high performance and high speed operation based on the increasing size and the intricacy of the system. Ont the basis of these techncial requirements, a plurality of programmable controllers have been recently installed for a large system provided with an intricated structure so as to carry out separately group control thereof. With the separate type control system, since it is necessary to establish an interlocking relationship between separate programmable controller groups, data linking means therebetween has been required.
FIGS. 1 and 2 represent examples of a data linking system using a conventional technique in which FIG. 1 represents the manner of linking for a parallel link provided by mutually connecting a plurality of programmable controllers PC1, PC2, PC3, . . . PCN. In order to establish the data link between optional programmable controllers PC1 to PCN in this manner, memory areas MA1 to MAN provided for respective input/output areas, or inner relays or the like of the programmable controllers are split into N numbers of memory area groups which are to be allocated to the respective programmable controllers thereby to establish the fixed link therebetween in which the memory areas MA1 to MAN can always accurately correspond to the programmable controllers, respectively. However, in this linking manner, since memory areas each having the same capacity are allocated to the respectively corresponding programmable controllers regardless of the frequency of the linkings, this manner does not economically utilize the hardware, and may cause a case where memory areas which are not substantially utilized are provided when the frequency of the linking is low, thus being not economical. In addition, in a case where a large number of the programmable controllers constituting a system are to be provided, the whole memory capacity therefor is extremely increased as well as increasing the number of memory areas actually substantially not utilized. This will cause time loss in the data transferring time. In order to eliminate this problem, when the memory areas are made small, the link between the respective programmable controllers are freely established. Moreover, since the fixed area type of link is adapted, it is necessary to arrange the sequence programs so as to input or output signals into or from the predetermined memory areas. This may cause a loss in the programming operation.
FIG. 2 represents another type of linking in which a plurality of programmable controllers PC1 to PCN are operatively connected to one master controller MC which is provided with a memory area MA including all link areas of the respective program memories and the memory area MA is allocated to the link areas of the programmable controllers, respectively. According to this arrangement, it is possible to establish the linking of all the programmable controllers PC1 to PCN through the master controller MC, but the direct linking between the respective programmable controllers PC1 to PCN is prohibited. In addition, the linking is performed through the memory area MA of the master controller MC, so that the number of the linking means are naturally limited.